Hepatobiliary cystadenoma is an uncommon lesion that is difficult to diagnose preoperatively. Here we report a 34-year-old woman who presented with enlargement of a cyst that had been observed for the previous 6 months. Diagnostic imaging revealed a 7-cm diameter cystic mass with irregular multiple septation in her liver. All laboratory test results were normal except for serum carbohydrate antigen (CA) 19-9 (62.5 U/ml). Because of the malignant potential and the history of enlargement, a complete surgical excision was performed. The patient was discharged after a good recovery; 2 months after surgery her serum CA19-9 level had returned to normal (32.9 U/ml). Regardless of the diagnostic modalities used, cystadenoma and cystadenocarcinoma cannot be differentiated with accuracy. Therefore complete surgical resection is the recommended therapy.